1. Field of the Invention
The present invention relates to a vehicle internal combustion engine having a crankshaft, a main shaft, a counter shaft and an output shaft arranged in parallel.
2. Description of Background Art
An internal combustion engine is known wherein a crankshaft, a main shaft, a counter shaft and an output shaft are arranged in parallel in a crankcase vertically halved into an upper case member and a lower case member. In this vehicle internal combustion engine, the crankshaft is provided at a mating surface of the crankcase. The main shaft is disposed vehicle-rearward of the crankshaft and above the mating surface of the crankcase. Main shaft-side driven gears, adapted to receive the power of the crankshaft transmitted thereto, are installed on the main shaft. The counter shaft, adapted to receive the power transmitted thereto from the main shaft, is disposed vehicle-rearward of the crankshaft and on the mating surface of the crankcase. In this way, the anteroposterior length of the internal combustion engine is made short. In addition, an output shaft is adapted to receive the power transmitted thereto from the countershaft and is disposed vehicle-rearward of the counter shaft. See, for example, Japanese Patent Laid-open No. 2000-343968.
However, in the conventional configuration described above, the main shaft-side driven gears secured to the main shaft have very large diameters; therefore, the crankcase protrudes upward, which causes restriction on the arrangement of auxiliaries, etc.